Symbol size in ggplot: scale_size_manual doesn't work

Question

I want to make some symbols in a figure bigger than the others. I found one solution, scale_size_manual, but it doesn't seem to have any impact.

Perhaps related, I also want to change the order of items in the legend. Again, the solution I found, guides(fill = guide_legend(reverse=TRUE), doesn't do anything.

#Fake data for this example
names <- c(rep("Other",8),rep("Porcupines",4),rep("Vipers",4), rep ("Pigs", 4))
rates <- runif(20, min=0, max=2)
sizes <- runif (20, min=0.1, max=5)
data <- data.frame (names, rates,sizes)

ggplot(data, aes(x=rates, y=sizes, group=names))+
    theme_classic(base_size = 14, base_family = "") +
    geom_point (aes(colour = names))+
    scale_colour_manual("Animal",values=c("blue","red", "green", "#0099FF"))+ 
    xlab ("Size")+
    ylab ("Rate")+
    scale_size_manual (values= c(1,2,2,2))+
    guides(fill = guide_legend(reverse=TRUE))

As mentioned above, the last two lines don't seem to be doing anything. Why not? Is there another way to change the symbol size of just some of the data (to make those points stand out)?

Answer 1

I think you need to add size as an aethetic. Try aes(x=rates, y=sizes, group=names, size=names) and you'll see scale_size_manual() kick in.